Spatial S-R compatibility with orthogonal stimulus-response relationship

Spatial stimulus-response (S-R) compatibility with unimanual two-finger choice reactions was investigated under conditions in which the spatial orientation of response keys was either parallel to or perpendicular to the orientation of the stimuli. Subjects responded to green or red lights in the left or right visual field (irrelevant stimulus location). The response keys were oriented horizontally on the left or right side of the body midline parallel to the stimuli, and were pressed with the palms facing down (Condition A), or were oriented orthogonally to the stimuli in the midsaggital plane, either horizontally and pressed with palms facing down (B) or facing up (C), or vertically and pressed with palms facing the body (D). The results for Condition A demonstrate the usual spatial S-R compatibility effect between field of stimulation and spatial position of responding finger. For Conditions B and D, a strong reaction time advantage still obtained for those stimulus-finger pairings that are compatible under Condition A. Condition C revealed an RT advantage for the opposite pairings. This shift of the compatibility effect from Condition B to Condition C indicates that the left/right distinction of fingers does not follow a simple, fixed spatio-anatomical mapping rule. The results are discussed within the framework of a hierarchical model of spatial S-R compatibility, with spatial coding and spatio-anatomical mapping as factors.     

Automatic imitation and spatial compatibility in a key-pressing task

Automatic imitation has been often confounded with spatial compatibility effects. Heyes (2011) called attention to this confound, and proposed some criteria which must be satisfied before these effects could be unequivocally taken to be an index of the functioning of the human mirror system. Evidence satisfying such criteria has been reported by Catmur and Heyes (2011), using a relatively unfamiliar finger abduction movement. However, because many previous studies relied on more familiar actions, we aimed at testing whether analogous effects could be obtained with a more practiced key-pressing task. In Experiment 1, we used anatomical controls (i.e., views of right vs. left hands) under conditions affording mirror imitation, and showed that spatial compatibility masked the effects of automatic imitation. Experiment 2 used rotated conditions to control for this spatial-anatomical confound, and it showed unequivocal effects of automatic imitation, which were obtained regardless of its relation to the spatial stimulus-response mapping. These results cast some doubts on the interpretation of previous reports relying exclusively on scenes presented from a mirror perspective, and suggest the convenience of using both rotated scenes and anatomical controls in order to assess automatic imitation.     

S-R compatibility effects due to context-dependent spatial stimulus coding

Responses are faster with spatial S-R correspondence than with noncorrespondence (spatial compatibility effect), even if stimulus location is irrelevant (Simon effect). In two experiments, we sought to determine whether stimuli located above and below a fixation point are coded as left and right (and thus affect the selection of left and right responses) if the visual context suggests such a coding. So, stimuli appeared on the left or right eye of a face’s image that was tilted by 90° to one side or the other (Experiment 1) or varied between upright and 45° or 90° tilting (Experiment 2). Whether stimulus location was relevant (Experiment 1) or not (Experiment 2), responses were faster with correspondence of (face-based) stimulus location and (egocentrically defined) response location, even if stimulus and response locations varied on physically orthogonal dimensions. This suggests that object-based spatial stimulus codes are formed automatically and thus influence the speed of response selection.     

Perception-action coupling and S-R compatibility

How is an aiming movement toward a visual target amended when the target suddenly steps to a new position just before or after the movement has started? Three hypotheses are examined: (1) the initial movement needs to be actively terminated before the new movement can be planned and executed, (2) substitution of the initial target position code results, after a normal RT, in the simultaneous termination of the initial movement and initiation of the movement to the new target position, or (3) a second movement from the initial to the second target is initiated after a normal RT, and superimposed on the ongoing movement toward the initial target. The substitution hypothesis assumes a highly continuous and parallel mode of operation of the perceptual-motor system, whereas the other hypotheses assume a distinctly discrete mode of operation. Detailed analyses of double-step movement trajectories clearly favored the substitution hypothesis. These results are discussed with reference to current views on motor control, overlapping-task performance, and the discrete-continuous issue. It is argued that the nature of the perception-action interface depends on the ideomotor compatibility of the task. Perceptual and motor processes operate in a highly continuous and parallel fashion in ideomotor compatible tasks, whereas the interposition of a limited-capacity response selection mechanism results in a discrete and intermittent mode of communication between these processes in non-ideomotor compatible tasks.     

S-R compatibility and response selection

In serial stage models, perception and action are usually thought to be linked to each other by an S-R translation mechanism. However, phenomena of S-R compatibility suggest a more direct relationship between perceptual and action domains. We discuss behavioral and psychophysiological evidence that irrelevant stimulus information automatically activates response codes, but then decays over time.

In a series of reaction time studies and electrophysiological experiments, we investigated both temporal and functional properties of the assumed automatic response activation process. We found that the amount of interference due to irrelevant spatial information depends upon how long its availability precedes that of the information relevant for response selection. This indicates that response activation decays rather quickly. If response-relevant and irrelevant spatial information are simultaneously available, electrophysiological measurements show that automatic activation of the spatially corresponding response rises soon after stimulus onset, but then dissipates and gets replaced by the activation of the response indicated by the relevant stimulus attribute.

We conclude that these findings do not support a pure translation account, but rather suggest the presence of two parallel and (at least partially) independent routes from perception to action: A direct route, allowing for automatic activation of response codes if stimulus and response features overlap, and an indirect route linking S and R codes in an arbitrary manner. Via the direct route responses may be primed independent of task-specific contingencies, while the correct response is selected via the indirect route. This use suggests that (a) the transmission of stimulus information to response stages does not (fully) depend on task relevance and that (b) different stimulus features can be transmitted asynchronously and independently from one another.     

Egocentric and relative spatial codes in S-R compatibility

Summary It has been shown that spatial compatibility is due to a comparison between the spatial codes that describe stimulus and response positions. Such codes are often defined in right-left terms. There are, however, two types of right-left codes that can be used for describing a position in space. One is formed with relation to the egocentric axes and can be termed side, whereas the other is formed with relation to an external reference location and can be termed relative position. Five experiments were conducted to determine the role of these different codes in producing spatial compatibility effects. In Experiments 1 and 2 the position of the stimulus provided the relevant cue for choosing the correct response (i.e., the situation was typical of spatial compability proper), whereas in Experiments 3, 4, and 5 the stimulus provided a locational cue that was not necessary for choosing the correct response (i.e., the situation was typical of the Simon effect). The experimental manipulations concerned the task demands and the time elapsing between availability of the stimulus code and availability of the response code. The results showed that upon stimulus presentation, both stimulus codes (that concerning side and that concerning relative position) were formed, but experimental manipulations determined the one that was effective in yielding compatibility effects. When the task required the use of one type of code, then spatial compatibility depended on that code alone. When the two coding processes were separated in time, then spatial compatibility depended only on the code that was formed simultaneously with the response code.     

Noise, S-R compatibility and hand dominance

The present study investigated the importance of task parameters in determining the effects of noise on performance, with interest focusing on variables which influence response selection and execution. The results of the first experiment showed that noise had an effect on response selection, slowing reaction times when an incompatible response had to be made. In contrast to this, the second experiment showed that noise had no effect on the speed of controlled movements and did not change the difference between movements made with the preferred and non-preferred hands.     

S-R compatibility and changes in RT with practice

A visual, two-choice RT experiment was performed to assess the effect of practice on compatibility effects. The data are interpreted as showing that identification of the position of the hand gradually becomes independent of the hand's normal side.Further analysis suggests that “compatible” or “natural” relationships are those in which a single recoding process can be successfully applied to all the relevant spatial relationships. This gives rise to the further prediction that where all relationships are uniformly “incompatible”, performance will be better than where there is a mixture of “compatible” and “incompatible” relationships.     

The relation between response-specificity, S-R compatibility, foreperiod duration and muscle-tension in a target aiming task

Three experiments are reported aiming at a further understanding of the effect of response-specificity, operationalized as the degree of commonality of direction of movements. In a previous study, Spijkers (1987) has claimed that response-specificity affects the readiness of the motor system and is not related to response-selection processes. These suppositions were generally confirmed in experiments 1 and 2 respectively. Common to both experiments were the variables average movement velocity and response-specificity. In experiment 1 the effect of the additional variable foreperiod duration was found to interact with that of response-specificity, hereby confirming its expected relation to the muscular system. The effect of response-specificity did not interact with that of spatial S-R compatibility in the second experiment, but also failed to show a main effect. The third experiment examined the supposed relation of response-specificity more directly through manipulation of the muscle-tension of the responding limb. The predicted form of the interaction between the effect of response-specificity and muscle-tension was confirmed which provided additional evidence for the interpretation of response-specificity effects in terms of differential muscular activation.     

The representation of pitch in auditory imagery: Evidence from S-R compatibility and distance effects

In three experiments we explored the nature of representations constructed during the perception and imagination of pitch. We employed a same–different task to eliminate the influence of nonauditory information and to minimise use of cognitive strategies on auditory imagery. A reference tone of frequency 1000, 1500, or 2000 Hz, or an imagined tone of a pitch indicated by a visual cue, was followed by a comparison tone (1000, 1500, or 2000 Hz) to which either a speeded same or different response was required. In separate experiments, same–different judgements were mapped to vertically (Experiments 1 and 2) and horizontally arranged responses (Experiment 3). Judgements of tones closer in pitch yielded longer reaction times and higher error rates than more distant tones, indicating a pitch distance effect for perceptual and imagery tasks alike. In addition, in the imagery task, same–different responses were faster when low-pitched tones demanded a bottom or left key response and high-pitched tones a top or right response than vice versa, suggesting that pitch is coded spatially. Together, these behavioural effects support the assumption that both perceived and imagined pitch are translated into an analogical representation in the spatial domain.     

Children's understanding of directed motion events in an imitation choice task

We investigated children’s understanding of directed motion events using an imitation choice paradigm. A total of 34 children (mean age 33 months) watched a model act out an event containing a manner of motion (hopping or sliding), a motion path (up or down a ramp), and a goal (in or on a bowl). On the children’s apparatus, the locations of the goal objects were different from the model so that the children needed to choose whether to imitate the path or the goal of the model’s event. Children’s choice of which component to imitate, therefore, reflects how they prioritize these event components. Most children showed no bias to imitate the goal of the event and, instead, preferred to imitate the model’s path at the expense of the model’s goal. However, children who spontaneously played with the goal objects during a free play session showed a diminished path preference, choosing to imitate path and goal components equally often. We suggest that children’s prioritization of information within an event depends on how that information is structured within the event itself.